Trampoline is a relatively new Olympic sport, making its debut in 2000. The competition format is three routines over two rounds.

In the first round, qualifying, a trampoline athlete performs a compulsory routine of eight relatively simple skills judged only in execution, followed by two complex skills to be judged on both execution and difficulty. Then they perform a voluntary routine, in which every skill is judged on both execution and difficulty. A time of flight score, an electronically measured record of actual time spend in the air, is the third component of both scores.

16 women will participate in in the qualifying round, but only eight will advance to the final. There, the scores will be wiped clean and they’ll perform just one voluntary routine. The athlete with the highest score (execution + difficulty + time of flight) wins.

The U.S. has one representative in the today’s women’s trampoline event, Nicole Ahsinger. A 2014 Olympian, Ahsinger originally competed in multiple gymnastics disciplines–trampoline, tumbling and double mini trampoline–before deciding to focus on just trampoline.

She was 33rd at the her first world championships in 2015, and the Olympic berth was won by a different athlete, Charlotte Drury. But when Drury broke her foot the day before the national championships, the U.S.’ main Olympic selection event, Ahsinger stepped up to win the spot.

Ahsinger will perform second in the qualification round.

The top athletes to watch are Rosie MacLennan, He Wenna and Li Dan. The three will perform in a row in the second half of the round.

MacLennan is the reigning Olympic champion, and has already received a great honor in Rio. She was chosen to be Canada’s flag bearer in the Parade of Nations and lead her country into the Opening Ceremony. MacLennan was the only Canadian athlete to win a gold medal at the 2012 London Olympics.

That won’t be the case here; Canadian swimmer Penny Oleksiak tied for gold in the 50m freestyle last night.

China’s He was the 2008 Olympic champion and won bronze in 2012. Her nickname is the “Trampoline Princess” but she failed to qualify for the individual final at the 2015 World Championships.

Instead it was Li, also from China, who took the title. She also won bronze at the 2013 Worlds and will be making her Olympic debut in Rio.